The invention generally relates to turn-up bladders used in the tire building process. More specifically, the invention relates to bladders having non-stick rubber surfaces for turning over uncured tire plys.
Tire building machines use annular inflatable rubber bladders to turn up the ends of plys of tires. During the turn-up operation, the uncured ply material is wrapped around and over the bead rings and against itself. Because the rubber ply material is tacky, the uncured ply material sticks to itself when the inflatable bladder doubles it over the beading ring.
Turn-up bladders traditionally have been made from vulcanized rubber (natural, synthetic or mixtures of the two) that has the undesirable characteristic of sticking to the tacky uncured tire plies when making contact with the uncured ply during the turn-up operation. Such momentary adhesion is especially destructive because the bladder exerts pressure against and, subsequently, away from ply. This adhesion results in possible defects to the tire ply and, after periodic use, premature deterioration of the bladder surface.
Initial attempts to deal with the problem of the bladder sticking to the ply during the tire building operation have met with only limited success. One early attempt involved applying a layer of non-stick rubber to the portion of the periphery of the bladder body contacting the ply end. Unfortunately, while the non-stick rubber did not stick to the ply, it also did not sufficiently adhere to the bladder body. After repeated operations, the non-stick rubber would begin to separate from the bladder body.
A later, alternative approach to the problem is described in U.S. Pat. No. 4,381,331 ("the '331 patent"). That patent teaches replacing the non-stick surface rubber with a fabric having reduced adhesion to uncured rubber. The fabric is embedded in a portion of the bladder surface. This attempted solution has the disadvantages of the fabric fibers on the bladder surface becoming frayed and of the cords separating from the bladder body after extended use.
It is an object of the present invention to provide a bladder having a non-stick rubber surface layer that will have improved adhesion to the bladder body and reduced tendency to separate from the bladder body during use.
It is another object of the present invention to provide a non-stick ply turn-up bladder without exposed fabric cords that could fray or separate from the bladder body during use.
It is a further object of the present invention to provide an improved ply turn-up bladder with increased adhesion of a non-stick rubber surface layer to the bladder body, such that the useful life of the bladder is increased.
It is yet a further object of the present invention to provide a method of making a bladder having a non-stick rubber surface with the above-listed desirable characteristics.